The present invention has for its object a process for making liquid crystal cells. These cells find use in the manufacture of display apparatus.
A liquid crystal cell is generally made up of a film of liquid crystals positioned between two wafers of glass covered with conducting deposits which are transparent or reflecting. These deposits play the role of electrodes and define the alpha-numeric characters or other characters that are to be displayed. A thin wall of a thickness of about one 10th of a micron is located between the two wafers and around the electrodes to provide the desired separation and insulation between the two wafers and to seal the cell.
Manufacture of such a cell has several problems. The wall must have a constant thickness to maintain good parallelism between the two wafers to obtain correct electro-optical performances both in the static regime and in the transatory regime. The filling of the cell with the liquid crystal must avoid all pollution or formation of bubbles. The sealing between the elements of the cell must be of good quality to obtain perfect tightness which determines the length of the life of the cell.
In known liquid crystal cells the wall is of a material of the epoxy-resin type which polymerizes at about 400.degree. C. In accordance with the known art, a thin layer of this product is deposited around one of the two wafers. The two parts of the cell are then applied one on the other and raised to a sufficiently high temperature so that the resin polymerizes. Filling is carried out by lightly heating the cell, first placed under vacuum, filling the cell through an opening in the layer of resin in one side of the cell and then closing the opening in the layer of resin. The final sealing of the cell consists in closing the opening by an appropriate plug.
This process of manufacture has several inconveniences. The two principal ones are that the process is not an acceptable industrial manufacturing process and the process does not provide cells having closely reproducible characteristics from one cell to the next and this introduces great difficulties in the control of the cells relating to a single display panel.